What are the effects of breathing helium gas on humans?

Answer 1

Breathing helium has no immediate harmful effects for humans because helium is an inert gas, and thus doesn't react with the body's biochemistry.

The danger comes from a continued session of breathing helium, especially in high concentrations. Since the helium replaces the air inside the lungs, there's the danger of hypoxia (lowered oxygen intake) if you don't flush out your lungs by taking in fresh air between sips of helium.

Symptoms of hypoxia include nausea, dizziness and fainting. The fastest way to recover is the same as for carbon monoxide, or any other noxious gas: expose the victim to fresh air, and possibly pure oxygen, ASAP.

The physiological effect of breathing helium, and the reason so many people try it, is that the gas, being less dense than air, causes sound waves to travel faster. The acoustic properties of the volume where the sound vibrations are made is thus changed. The net effect is that your voice sounds higher in pitch, gradually descending back to normal as the helium exits your lungs.

Answer 2

Breathing helium can displace oxygen in the lungs, leading to hypoxia (low oxygen levels) and potentially causing dizziness, loss of consciousness, and asphyxiation. Inhaling helium for fun or for a prolonged period can be dangerous and should be avoided.